This invention relates to electro-hydraulic control mechanisms for use in automatic shifting power transmissions and, more particularly, to fly-by-wire control mechanisms.
Many of the currently-available high performance planetary transmissions utilize what has been termed clutch-to-clutch shifting. This term indicates that the ratio interchange is performed by disengaging one plate-type friction device while engaging another plate-type friction device. This is accomplished without the use of one-way devices. Therefore, the overlap control must be quite accurate to prevent any disruption in the power flow from the transmission input to the transmission output.
At least one planetary transmission that is utilized with clutch-to-clutch shifting controls is shown in U.S. Pat. No. 4,070,927, issued to Polak on Jan. 31, 1978. This transmission is equipped with solenoid controlled trim valves that are actuated by electronic control units to provide engagement and disengagement pressures for the torque transmitting friction devices within the transmissions. One such solenoid control system is shown in U.S. Pat. No. 5,601,506, issued to Long et al. on Feb. 11, 1997. Also, the transmissions in this category desire to use what is known as skip-shifting, that is, a first-to-third ratio interchange or a second-to-fourth ratio interchange, etc. The above-identified patent to Long et al. does not provide for skip-shifting.
It is also desirable to ensure that the vehicle incorporating the transmission can return to a repair unit in the event of the discontinuance of electrical power. This is known as limp-home capability. Two such currently-known patents provide limp-home capabilities for power transmissions, one of which is U.S. Pat. No. 4,827,806, issued to Long et al. on May 9, 1989, and U.S. Pat. No. 5,616,093, also issued to Long et al. on Apr. 1, 1997.
The above-identified patents issued to Long et al. utilize trim valves in combination with shift valves to control the pressure within the on-coming and off-going friction devices. The trim valves are equipped with variable pressure solenoid valves while the shift valves are controlled by on/off type solenoid valves.
In order to reduce the use of shift valves, trim valves, such as that shown in Long et al., U.S. Pat. No. 5,911,244, have been provided as control features which require only a single trim pressure, that is, a variable solenoid valve, to be utilized in controlling the shift valve so as to provide a variable brake pressure increase to the on-coming friction device.
These types of variable pressure trim valves have been proposed for power transmission controls as disclosed in co-pending U.S. Ser. No. 10/025,232, filed Dec. 19, 2001, which is assigned to the assignee of the present application.
All of the above-described electro-hydraulic control systems require the use of a manually-operated control valve wherein a direct mechanical connection between the operator and a valve controlling forward, reverse and neutral operating conditions is provided.
It is an object of the present invention to provide an improved electro-hydraulic control mechanism for a multi-speed power transmission having a fly-by-wire control system.
In one aspect of the present invention, electro-hydraulic control has a pair of logic valves, a system pressure regulator valve, and a control pressure regulator valve for selectively distributing a bias control pressure to the system regulator valve through one of the logic valves.
In another aspect of the present invention, the bias control pressure is distributed to a bias area and a system regulator valve when the one logic valve is in a pressure set position.
In yet another aspect of the present invention, a variable bias pressure is selectively distributed from a trim pressure control valve through both of the logic valves to the bias area on the system pressure regulator valve.
In still another aspect of the present invention, the variable bias pressure is distributed only when one logic valve is in a spring set position and the other logic valve is in a pressure set position.
In yet still another aspect of the present invention, the electro-hydraulic controls provide for the selective distribution of engagement pressure with two torque transmitting mechanisms from one trim control valve.
In a still further aspect of the present invention, the electro-hydraulic control will establish the third forward ratio if the electro-hydraulic controls are discontinued during normal operation in first through fourth forward drive ranges or ratios.
In yet still another aspect of the present invention, the electro-hydraulic control will establish the fifth forward ratio if the electronic portion of the controls is discontinued during normal operation in the fifth or sixth forward drive ratio.
In still another aspect of the present invention, one of the logic valves incorporates a bias pressure from one of the torque-transmitting mechanisms which maintains the logic valve in a spring set position until the torque-transmitting mechanism is disengaged.
In still another aspect of the present invention, the pressure bias logic valve provides the capability to distribute control pressure to two torque-transmitting mechanisms from a single trim valve.